1. Field of the Invention
The present invention relates to a rotation detecting device and an automobile with the same, and more particularly, to a rotation detecting device suitable for detecting a rotation angle of one or more rotations of a rotary body and to an automobile comprising the rotation detecting device as a steering angle sensor of a steering wheel.
2. Description of the Related Art
Conventionally, a technique is known in which a rotation detecting device is provided between a steering shaft and a body of an automobile, and the control of a damping force of a suspension, the control of a shift position of an automatic transmission, and the steering control of rear wheels in a four-wheel steering vehicle are performed on the basis of the steering angle, steering speed, and steering direction of a steering wheel detected by the rotation detecting device.
The steering wheel (the steering shaft) is configured to rotate one or more in the right and left directions from its neutral position. Therefore, in order to detect the steering angle of the steering wheel, a rotation detecting device is used which is constructed by a combination of an absolute type encoder that detects a rotation angle of one or more full rotations and an incremental type recorder or an absolute type encoder that detects a rotation angle of less than one full rotation.
Conventionally, these kinds of rotation detecting devices include, for example, the following devices:
(1) a rotation detecting device comprising: a rotor member that rotates together with a code disc constituting a part of an incremental type encoder; a stator member that rotatably supports the rotor member; a relay gear journalled to the stator member; a rotating member that constitutes a part of an absolute type encoder that is arranged concentrically with the rotation center of the rotor member; and rotation angle detecting elements for detecting a rotation angle of the rotating member, wherein the relay gear is caused to intermittently mesh with engaging protrusions provided on the circumferential surface of the rotor member, and is caused to always mesh with a driven gear provided in the rotating member, the rotating member is rotated only in the period when the relay gear meshes with the engaging protrusions during the rotation of the rotor member, and the detecting elements detect a change in the rotation angle of the rotating member (for example, see Patent Document 1),
(2) a rotation detecting device having an absolute type encoder and an incremental type encoder, wherein the absolute type encoder comprises a substrate having a resistance pattern, a decelerating rotary body having a brush to be brought into sliding contact with the resistance pattern, and a gear mechanism obtained by a combination of a plurality of gears that transmit the rotation of the steering wheel to the decelerating rotary body, and
(3) a rotation detecting device in which an absolute type encoder converts rotational motion of a steering wheel into linear motion of a driven body, and the rotation angle of the steering wheel is detected in accordance with the magnitude of linear motion of the driven body.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 10-227631 (see FIGS. 5 to 8)
The above-mentioned conventional rotation detecting devices have no problem in detecting a rotation angle of the rotary body.
However, in the rotation detecting device, as described in Patent Document 1, of the above-mentioned conventional rotation detecting devices, the relay gear is caused to intermittently mesh with the engaging projections provided on the circumferential surface of the rotor member. As a result, there are problems in that impact noise is easily generated whenever the relay gear meshes with the engaging projections, and the noise level becomes worse.
Further, in the rotation detecting device as described in Patent Document 1, a multi-stage gear mechanism obtained by a combination of three or more gears is required to increase the gear reduction ratio of the gear mechanism. Therefore, hysteresis is generated due to backlash of gears and the like and has an effect on the accuracy of detection, and a large space is needed for mounting the gear mechanism. As a result, there is a disadvantage in that the rotation detecting device is larger.
Moreover, in the rotation detecting device that converts the rotational motion of the steering wheel into the linear motion of the driven body, a motion conversion mechanism, such as a lead screw mechanism of gears, should be arranged in a circumferential direction of the steering wheel. Therefore, the number of parts is increased, thereby raising the manufacturing costs of the rotation detecting device, and a large space is needed for mounting a motion conversion mechanism. As a result, there is a disadvantage in that the rotation detecting device is large.